Field of the Invention
The invention relates to a circuit configuration for offset compensation, including a filter device for ascertaining a direct component in an input signal delivered to it and a linking device for subtractive linking of the input signal and an output signal of the filter device.
One such circuit configuration is known, for instance, from the corporate publication by Linear Technology Corporation, entitled: Linear Applications Handbook 1987, page AN21-1. In the circuit configuration described therein, on one hand the input signal is carried directly to an inverting input of an operational amplifier and on the other hand it is applied, with the interposition of a low-pass filter, to a noninverting input of the operational amplifier. The low-pass filter has a relatively low limit frequency, so that essentially only direct components reach the noninverting input of the operational amplifier. It is accordingly through the use of the low-pass filter that the direct current operating point adjustment of the operational amplifier is carried out, while the actual signal path extends through the inverting input.
However, when direct components are large it is problematic that the operational amplifier is overdriven in terms of direct current and accordingly requires a longer transient recovery time. In order to prevent that, in the known circuit configuration a voltage divider precedes the noninverting input of the operational amplifier. Often, however, it is necessary that the offset compensation function as precisely as possible up to the limit of the operating range of the operational amplifier and be sharply limited outside the operating range. Moving any farther away from that limit would only make the transient recovery time worse, and any nonlinearity near the range limit would lead to inaccuracies. Those demands, however, cannot be met with a voltage divider as in the known circuit configuration.